In August 1980 the principal investigator was recruited (from Vanderbilt University, Nashville, Tennessee) to take a permanent position at the NCI and establish a cell biology group which would simultaneously perform independent research and collaborate with and provide a resource for the Laboratory of Tumor Virus Genetics in the Division of Cancer Cause & Prevention. During the past year, a group of well trained individuals dedicated to accomplishing these objectives has been assembled. A number of collaborative and independent studies have been initiated and significant findings have already begun to emerge from the efforts of this group. Our approach to the cell biology of carcinogenesis is multifaceted and attempts to integrate information concerning tumor induction by chemicals, viruses, or radiation. Four related studies are described. Study 1. Effects of environmental carcinogens on hemopoietic stem cells. Study 2. Characterization of a "new" putative regulatory protein. Study 3. Mechanism by which retraviruses bring about increased hormone sensitivity and increased cell proliferation. Study 4. Testing the generality of the "SISTER" hypothesis: A hormonal approach to understanding and treating cancer.